Solvent refining of petroleum oils



Patented Nov. 29, 1938 UNITED STATES- PATENT OFFICE v 2,188,188 sonvsmasmmc. or rnraomuu oms Arthur W. Hixson, Leonia, N. 3., and RalphMiller,

New York, N. Y., assignors to The Chemical Foundation, Incorporated, acorporation of Delaware No Drawing; Application November 0, 1937. SerialNo. 113,194

15 Claims.

and fuel oil fractions. the same general complexity obtains, althoughthe respective percent- 15 ages of the diii'erent groups in suchcommercial fractions may vary. Thus, a typical relatively high boilingrange distillate, having'the characteristics of lubricating oil,contains parafflnic, naphthenic, and aromatic constituents and some 20asphalt, the respective proportions of such constituents dependinglargely on the type or source of the crude 011. Thus, Pennsylvania'oilcontains little or no asphalt and a relatively small amount ofaromatics. The Coastal oil, con- 25 versely, has a relatively higherpercentage of asphalt and aromatics than the Pennsylvania oil.

For certain uses, it is desirable to preferentially remove certain ofthese constituents from the 30 homogeneous mixture, either for thepurpose of improving the residuum forsome special purpose or forutilizing the extracted fraction for another use. Thus, it is known thatfor most purposes the heavier paraflinic fractions constitute the 35best lubricants, especially for high temperature lubrication such as isrequired in the modern internal combustion engine. On the other hand,

it is likewise known that the more paraflinic lighter fractions, in thegasoline range, present 40 a decidedly greater tendency to knock than dothe more oleflnic gasolines. It is, therefore, sometimes desirable totreat, say, a vapor phase cracked Mid-Continent gasoline so as topreferentially extract the olefinic constituents so that 45 they maysubsequently be employed to blend with other gasolines toincrease theoctane rating of such gasolines.

It has been proposed heretofore to subject complex mixtures of thesehydrocarbon oils in the 50 lubricating and gasoline range to the actionof solvents whichhave a preferential amnity for the non-parafiinicconstituents so as to obtain an extract and/or a ramnate respectivelyricher in the desired type of oil than the original stock.

55 It is known that (by choosingthe proper solvent) it is theoreticallypossible to preferentially dissolvethe naphthenic and aromaticconstituents, to segregate the solvent with its dissolved nonparaiiinsfrom the residual oil and separately to recover the residual oil orrafilnate of a relatively I higher paraflinicity, and an extractfraction of a relatively lower paramnicity, than the original 'oil whichwas treated.

This result, although theoretically quite possible, has been difficultto achieve on a commercially satisfactory basis. The workers in the arthave been active on this problem for over a decade and althoughliterally hundreds of solvents or solvent mixtures have been suggestedbut a very few have attained commercial use. 0f the greater numbercfthese extractants that have been proposed, the only ones that havegone into any substantial commercial use are; nitrobenzene, aniline,phenol, sulphur dioxide and benzene, furi'ural, B B dichloroethyl ether,and mixtures of cresol, phenol and propane. Each of these solvents, orsolvent mixtures, present certain advantages, but they also presentinherent disadvantages.

The reason why such a relatively few number of solvents actually havebeen employed out of the vast number suggested lies in the fact that thecriteria of commercial values are verydifficult to meet. In the natureof its use, the

quantity of the solvent employed runs into large figures and actuallymay be calculated on a tonnage basis. For this reason the price of thesolvent is a factor of dominant importance; too high a solvent cost ispositively inhibitive to commercial employment, whatever may be thetheoretical emcacy of extraction and the theoretical recovery of thesolvent, for, in actual plant operation, some solvent loss isinevitable. This factor of high cost rules out a great many otherwisesatisfactory solvents, particularly the 40 more complex organiccompounds.

In addition to this important factor of initial cost, there are otherfactors of a chemical or physicochemical nature which characterize theideal selective solvent and which are extremely diflicult to discoverembodied in a commercially available compound. For example, certainsolvents suggested in the past, although possessing a. satisfactory high.selectivity, present a low solubility for the constituents which aredesired to be removed. In these circumstances, in order to extract suchnon-parafilnic constituents, a large and commercially excessive amountof such solvent must be employed. Yet again, certain solvents maypossess a satisfactory selectivity and' teristic which militates againsttheir use. For

example, such a solvent may have adensity which is so close to that ofthe oil being treated that segregation or stratification is'dimcult andcostly. Other factors which characterize the ideal solvent are: adesirably low melting point, a relatively low boiling point, a markedtendency to stratify from the paraffinic fraction at separationtemperatures, a low solubility in water and an amenability to recovery,preferably by simple physical methods such as low temperature fractionaldistillation. It will thus be seen that, in

the very nature of this technical use, the field from which a,satisfactory selective solvent may be chosen is quite constricted.

As intimated above, one of the factors of major importance in the choiceof a selective solvent is a low initial solvent cost. For refineryoperations, such initial cost should, of course, be as low as possibleand, in any'event, should' not exceed a price of the order of 9 to 10cents a pound. Such solvent should, in conformity with the normindicated above, have a selectivity which is as high as possible andwhich is at least comparable to that of the solvents now employed. Suchsolvent also should have a relatively high density as compared with theoils to be treated, such as a lubricating oil fraction. Additionally,the solvent should have a high miscibility temperature, a boiling pointnot materially exceeding 200 C. and should be substantially insoluble inwater and stable under the conditions of use. A selective solvent whichwould satisfy these criteria would be superior to any now in commercialemployment.

With the above outlined stringent requirements in mind, the priorworkers naturally investigated the simple, readily available aliphaticcompounds. Considered as a class, however, such compounds were found tobe unsuitable. Similarly, the simpler, less expensive benzenederivatives were studied, but as indicated above, with but a very fewexceptions, these were found to be ineffective. While a multitude of themore complicated derivatives have been suggested in the literature, itis apparent to those skilled in the art that the price requirement inthis field is a definite limitation which rules out any such expensivesynthetic derivatives.

In view of these considerations, it is apparent that if a syntheticcompound is to be employed as a selective solvent, it must be producedfrom a starting material or mother substance that is relatively cheapand that, with this requirement, for all practical purposes the benzenederivatives, except for the simpler substitution products, are ruledout. It is also quite apparent that as an inexpensive source materialpetroleum products would be decidedly more preferable. In recent yearsthe potentialities of the parafiin hydrocarbons as a source material forthe production of substituted aliphatics has received considerableattention. For example, Haas and his colleagues (Ind. Chem. Soc, 28,339(1936) and U. S. Patent 1,967,667) describe a vapor phase nitration ofparaffin hydrocarbons for the production of nitro paraffins and indicatethat such end productsselective solvent for the fractionation of mineraloils. The potentialties of such compounds for use as selective solventshas previously been considered andthe patent literature describes theuse of nitro substituted parafilns as selective solvents. Aninvestigation of the characteristics of these simpler substitutionproducts, however, indicates their unsuitability for the purpose athand. As a typical example, the behavior of nitromethane is a case inpoint. When nitromethane (B. P. 101 C.) is mixed with an equalquantity'of Mid-continent oil having aviscosity of 48 Saybolt seconds at210 F. and a viscosity index of 57, and the mixture was heated in anattempt to insure miscibility, it was-found that the solvent boiledbefore complete miscibility was obtained, in fact, hardly any of the oildissolved in the solvent. This characteristic of too low a'boiling pointsubstantially precludes the use of this compound for the extraction oflubricating oils.

It might appear, theoretically, that the higher members of the serieswould operate, due to their higher boiling point and longer chainstructure. However, this does not prove to be the case for, as thelength of the chain increases, there is a corresponding decrease indensity so that, while the higher homologues may satisfy the requirementas to boiling point and miscibility with the oil to be processed, thedifferential in density which obtains is too small to insure thenecessary rapid stratification.

As the result of considerable experimentation in this field, it has beenfound that such cheap source material, that is to say, the parafiinhydrocarbons or their simpler derivatives, may be utilized for theproduction of substituted aliphatics which serve admirably as selectivesolvents. It has been found that as a broad proposition, while nitrosubstituted paraffins are unsuitable, certain derivatives are eminentlysuitable. Considered more specifically, it has been found that theintroduction of another substituent, particularly a halogen, in thenucleus, modifies the physical characteristics of the original compoundso as to render it most effective for the function of selec tiveextraction. It was found that, when a hydrogen of a nitroparaffin wasreplaced with a chlorine atom, the resulting nitrochloroparaffinpossessed a higher density and a higher boiling point than thecorresponding nitroparaflin, and that the modification of thesecharacteristics was of such a degree as to comply with the describedcriteria established for an effective selective solvent. The comparisonbetween nitropropane, for example, and its analogue, nitrochloropropane,clearly illustrates this beneficial modification of the physicalcharacteristics which are so important in this particular use. Whereasnitropropane has a boiling point of 131 C. and a density of 1.002 (25C.) nitrochloropropane, on the other hand, has a boiling point of 1723C. and a density of 1.224 (30 C.) Similarly, whereas nitrobutane has aboiling point of 139 C'. and a density of substantially .98, itsanalogue, nitrochlorobutane, has a boiling point of 181-8 C. and adensity of 1.187 (20 C.). a

It is thus clear that the marked increase in the boiling point anddensity is a constitutive property of the halogenated nucleus and servesto sharply differentiate the nitrochloroparaflins from the correspondingnitroparafiins in respect of their availability and utility as selectivesolvents.

As is known to those skilled in the art, the property of selectivity orpreferential solubility Fifty grams ofnitrochloropropane'were added to50 grams of a Mid-continent neutral oil having a viscosity of 268Saybolt seconds at 100' I". and a viscosity index of 57.7. The mixturewas heated above the miscibility temperature of 96 C. After completemiscibility had been obtained, the solution was allowed to cool, withoccasional agitation, in an oven maintained at C., at which temperaturethe two layers were separated. Each layer was then subjected to vacuumdistillation.

Upon' analysis (using an all-glass Fitsimmons suspended level viscometerand calculating the yield on the weight basis). it was found that 86 percent. of the original oil was in the raiilnate and that such rafilnatehad a viscosity of 239.9 Saybolt seconds at 100 F. and 46.1 Sayboltseconds at 210 F. and a viscosity index of 69.1. The oil layer containedbut 16 per cent. of the solvent.

It is luminously obvious that these results showthat'nitrochloroparaflins possess the property of marked selectivity aswell as the other beneficial properties such as satisfactory boilingpoints,

density and miscibility, which determine their commercial utility. Itwill be noted, in passing, that in the illustrative experiment, theyields are given in weight. Since the rafiinate has a lower, and theextract a higher specific gravity than the original oil, a comparisoncalculated on a volume basis will be numerically more favorable.

The series of compounds whichhave herein been described as selectivesolvents may be produced in any efiective or approved manner. Theprocedure may be by two diflerent general methods, each utilizing theparafilns as a source material. Such parafiins may be nitrated and theresulting nitroparaflins then halogenated. Again, the parafilns may bechlorinated and the chloroparaflins may be nitrated. Then again, ifdesired, the compounds mentioned herein may be produced with a synthesisstarting from the nitrdtilcohols.

For example, according to one method (see Konawalofl, Russian Journal ofPhysical Chemistry, 36, 22 (1904)) isobutyl chloride may be reacted withdilute nitric acid in a sealed tube at '70 to 80 C., from 12 to lfihoursand the unreacted chlorobutane separated and treated with additionalamounts of nitric acid. The formed nitrochlorobutane may be removed byfractional distillation. Or again, the nitrochloroparaffin may beprepared by the method outlined by Henry (Bul. Societe Chemique deParis, 3rd Series, 13, 999 (1885)); which consists essentially inproducing anitro alcohol by condensation of the corresponding aldehydewith a nitromethane group in the presence of a small amount of potassiumcarbonate, followed by the treatment of the nitro alcohol withphosphorus pentachloride to produce the nitrochloroparaflin.

A modification of the Henry method was utilized with good results. Underthe Henry synthesis, in the first stage of the reaction, the nitro 3 drypyridine and utilizing this" chloride 'as the chlorinating agent. Whenutilizing this modified reaction, it is advisable to add the chlorideslowly to the boiling mixture. The reaction products are preferablypurified by washing with water It will be understood that the methodsgiven are merely suggestive and are not given-as necessarily related tothe actual extraction of the oil. The invention is available foremployment with the described class oicompounds, or their equivalents,however such compounds may be produced.

It will be appreciated that within the broad concept of the invention arelatively largenumber of diiferent specific compounds may be used, thechoice of which will depend on the conditions of the particularextraction operation and/or on the characteristics of the oil fractionwhich is to be treated. The different solvents comprehended herein maybe used alone or in admixture with each other or with specificallydifferent solvents. Again. the improved solvents described herein may beused in conjunction with other known solvents for sequentialextractions.

It is particularly to be observed that the improved results disclosedherein are obtainable with the broad class of compounds described andare not limited to the particular compound cited in the example. Asexamples of other characteristic members of-the group may be mentioned,chioronitromethane, bromo nitromethane, a achloronitroethane, ab-chloronitroethane', a a adibromonitroethane, a a-chloronitropropane, aa-bromonitropropane, a-chloro-b-nitropropane,

leum oils containing parafllnic and non-parafiinic constituents, thestep consisting in separating the constituents by extracting with anitrochloroparaflin.

2. The process of solvent refining of petroleum oils containingparafflnic and non-parafllnic constituents, which comprises selectivelyextracting the non-parafllnic constituents with a halogen substitutednitroparafiln.

3. The process of solvent refining of petroleum oils containingpara'iiinic and non-parafilnic constituents which comprises, separatingsuch constituents by extracting the oil with a halogenatednitrogen-containing paraflin.

4. In the process of solvent refining of petroleum oils containingparamnic and non-parafiinic constituents the step consisting inseparating the constituents by extracting with a halogenatedmononitroparafiin. e

5. The process of solvent refining of petroleum oils containingparaifinic and non-parafiinic constituents which comprises separatingsuch constituents by extracting the oil with a chlorinatednitros'en-containing parafiin.

6. The process of solvent refining of petroleum 75 oils containingparafiinic and non-parafiinic constituents which comprises, separatingsuch constituents by extracting the oil with a chlorinatedmononitroparafiln.

. I. The process 01' solvent refining oi petroleum oils containingparafiinic and non-parafllnic constituents which comprises separatingsuch constituents by extracting the oil with a halogenated nitrcethane.

8. The process of solvent refining of petroleum oilscontainingparafilnic and non-parafiinic constituents which comprisesseparating such constituents by extracting the oil with a halogenatednitropropane.

9. The'process of solvent refining of petroleum oils containingparafiinic and non-paramnlc constituents which comprises separating suchconstituents by extracting the oil with a halogenated nitrobutane.

10. The process of solvent refining of petroleum oils containingparafiinic and non-parafilnic constituents which comprises, separatingsuch constituents by extracting the oil with chloronitroethane.

11. The process of solvent refining oi petroleum oils containingparafiinic and, non-parafiinic constituents which comprises separatingsuch constituents by extracting the i1 with chloronitropropane. I

12. The process 01' solvent refining of petroleum oils containingparamnic and non-parafilnic constituents which comprises, separatingsuch constituents by extracting the oil with chloronitrobutane.

13. The process of solvent refining of petroleum oils containingparafiinic and non-paraffinic constituents which comprises, separatingsuch constituents by extracting the oil with B-chloro l.- nitro propane.

14. The process oi solvent refining of pyrogenetically produced oilfractions containing paraflinic and non-paramnicconstituentswhichcomprises, selectively extracting the non-parafiinicconstituents with a chloronitroparaflln.

15. In the process of solvent refining oi pyrogenetically produced oilfractions containing parafiinic and non-parafiinic constituents the stepconsisting in separating the constituents by extracting with a selectivesolvent containing a nitrcchloroparafiin.

ARTHUR W. HIXSON. RALPH MIILER...

